When a product is assembled by a power tool or the like by repeatedly performing a screw tightening operation, and if checking the completion of a series of screw tightening operations solely relies on an operator, some of the screws may sometimes remain unfastened. Since occurrence of such case would lead to deterioration in quality and reliability of the product, the number of tightening operations needs to be checked in every operation process. Accordingly, excessive burdens are imposed on the operator though mistakes cannot be completely prevented.
To that end, there have been a number of proposals for inventions that are geared towards preventing forgetfulness of a screw tightening operation by using a controller that is connected to a power tool which counts the number of tightening operations (see, e.g., Japanese Patent Laid-open Applications Nos. H9-150338, 2003-123050 and 2005-125464).
Although the above prior art references can improve the drawbacks of forgetting the screw tightening operation, its applications are limited due to the fact that the power tool and the controller are connected with each other by a power cord. This problem may not be that serious when an operator is working in a restricted working area using a corded power tool or a pneumatic power tool connected to an air hose. However, when an operator is working in an unrestricted area, handling of tool and the controller would become troublesome, or restriction on the area where an operator can work may arise. Especially, in case of a cordless rechargeable power tool, the inherent advantages of the cordlessness diminish.
Therefore, the present inventors have proposed an idea of accommodating a control circuit in a main body of the power tool, for monitoring the screw tightening operations. Then, the control circuit is a precision electronic device so that the control circuit needs to be protected from impacts and vibrations. Accordingly, when a control circuit board is installed inside the power tool, a location of the board needs to be carefully chosen. Especially, when the power tool falls and collides against the ground, great impacts and vibrations may be given to the control circuit to be damaged. Therefore, it is critical to protect it from damage.